Murukanahally Kempaiah Devaraju

Direct Observation of Antisite Defects in LiCoPO4 Cathode Materials by Annular Dark- and Bright-Field Electron Microscopy

LiCoPO4 cathode materials have been synthesized by a sol-gel route. X-ray diffraction analysis confirmed that LiCoPO4 was well-crystallized in an orthorhombic structure in the Pmna space group. From the high-resolution transmission electron microscopy (HR-TEM) image, the lattice fringes of {001} and {100} are well-resolved. The HR-TEM image and selected area electron diffraction pattern reveal the highly crystalline nature of LiCoPO4 having an ordered olivine structure. The atom-by-atom structure of LiCoPO4 olivine has been observed, for the first time, using high-angle annular dark-field (HAADF) and annual bright-field scanning transmission electron microscopy. We observed the bright contrast in Li columns in the HAADF images and strong contrast in the ABF images, directly indicating the antisite exchange defects in which Co atoms partly occupy the Li sites. The LiCoPO4 cathode materials delivered an initial discharge capacity of 117 mAh/g at a C/10 rate with moderate cyclic performance. The discharge profile of LiCoPO4 shows a plateau at 4.75 V, revealing its importance as a potentially high-voltage cathode. The direct visualization of atom-by-atom structure in this work represents important information for the understanding of the structure of the active cathode materials for Li-ion batteries.

Novel processing of lithium manganese silicate nanomaterials for Li-ion battery applications

Lithium manganese silicate positive electrode materials have received great attention because of the two lithium ion capacities and can be realized in ultrafine nanoparticles due to their low volumetric changes upon lithium insertion and extraction. A supercritical fluid process has been adopted to synthesize monodisperse Li2MnSiO4 ultrafine particles and hierarchical nanostructures with a mean particle diameter of 4–5 nm and successfully shown to attain a high electrochemical performance. A reversible capacity (190–220 mA h g−1) of more than one lithium ion was obtained for the ultrafine monodisperse nanoparticles and hierarchical nanostructures with good cyclability. The enhanced cyclability was found to be due to the monodisperse nanoparticles, which provide a short length for Li-ion diffusion, and possess low volumetric changes. In addition, the varyingly sized Li2MnSiO4 particles were also synthesized via a supercritical fluid process. This process is simple, rapid, energy saving and broadly applicable to other functional materials.

Controlling the shape of LiCoPO4 nanocrystals by supercritical fluid process for enhanced energy storage properties

Lithium-ion batteries offer promising opportunities for novel energy storage systems and future application in hybrid electric vehicles or electric vehicles. Cathode materials with high energy density are required for practical application. Herein, high-voltage LiCoPO4 cathode materials with different shapes and well-developed facets such as nanorods and nanoplates with exposed {010} facets have been synthesized by a one-pot supercritical fluid (SCF) processing. The effect of different amines and their roles on the morphology-control has been investigated in detail. It was found that amine having long alkyl chain such as hexamethylenediamine played important roles to manipulate the shape of the nanocrystals by selective adsorption on the specific {010} facets. More importantly, the nanorods and nanoplates showed better electrochemical performance than that of nanoparticles which was attributed to their unique crystallographic orientation with short Li ion diffusion path. The present study emphasizes the importance of crystallographic orientation in improving the electrochemical performance of the high voltage LiCoPO4 cathode materials for Li-ion batteries.

A rapid hydrothermal synthesis of rare earth oxide activated Y (OH)3 and Y2O3 nanotubes

One-dimensional single crystalline rare earth ion (Tm(3+), Tb(+3), and Eu(3+)) doped Y (OH)(3) nanotubes with inner diameters of 20-110 nm, outer diameters of 50-140 nm, and 1-5 microm in length were prepared for the first time by a rapid hydrothermal method within a short reaction period (5 min) at subcritical temperature (320 degrees C) and high pressure (about 40 MPa). A temperature dependent nanostructure evolution study was performed under rapid hydrothermal conditions and the effects of other processing parameters such as concentration of KOH and reaction time were found to be key parameters for the formation of highly anisotropic crystal structures of rare earth hydroxide nanotubes. Rare earth ion (Tm(3+), Tb(+3), and Eu(3+)) doped Y(2)O(3) nanotubes can be obtained after calcinations above 450 degrees C. The luminescent property of rare earth doped Y(2)O(3) nanotubes was also explored and compared with reference samples prepared via a conventional co-precipitation method.

Solvothermal synthesis and characterization of ceria–zirconia mixed oxides for catalytic applications

Solvothermal synthesis under supercritical conditions (400 degrees C) and high autogenous pressure (about 40 MPa), has been carried out for the direct preparation of nanocrystalline powders of CeO2, Ce(0.85)Zr(0.15)O2, Ce(0.75)Zr(0.25)O2, Ce(0.65)Zr(0.35)O2 and Ce(0.5)Zr(0.5)O2 which are characterized for applications as catalysts for oxygen storage in automotive catalysis. The synthesis was carried out in the presence of polyethylene glycol and water. For the characterization, x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS) and the Brunauer-Emmet-Teller (BET) technique were employed. The oxygen storage capacity (OSC) of as-prepared and calcined samples without loading of noble metals was measured using thermogravimetric-differential thermal analysis (TG-DTA) at 600 degrees C with a continuous flow of CO-N2 gas and air alternately. Ce(0.5)Zr(0.5)O2 nanoparticles with a BET surface area of 102 m(2) g(-1) exhibited the highest OSC of 0.073 50 mol-O2/mol-CeO2. The OSC values obtained increased with increasing the amount of ZrO2 doping in the samples.

Synthesis of Li2CoSiO4 nanoparticles and structure observation by annular bright and dark field electron microscopy

Nanocrystalline Li2CoSiO4 particles have been successfully synthesized via a supercritical fluid process. The as-synthesized and heated particles were 50–250 nm in diameter and were well dispersed as observed by high resolution transmission electron microscopy (HRTEM). Energy dispersive spectroscopy (EDS) and elemental mapping by scanning transmission electron microscopy (STEM) show the purity and homogenous elemental distribution of the Li2CoSiO4 particles. The high resolution transmission electron microscopy (HRTEM) images show well resolved lattice fringes of the crystalline Li2CoSiO4 particles. The structure of the Li2CoSiO4 particles has been determined for the first time by annular bright field-scanning transmission electron microscopy (ABF-STEM) and high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The results revealed a tetrahedral arrangement of CoSiO4 in the Li2CoSiO4 structure. The electrochemical performance results support the idea that this material has potential as a positive electrode for use in a lithium ion battery.

Benzylamine-directed growth of olivine-type LiMPO4 nanoplates by a supercritical ethanol process for lithium-ion batteries

Olivine-type LiMPO4 (M = Fe, Mn, Co and Ni) cathode materials hold promise for next-generation of lithium-ion batteries and future applications as hybrid electric vehicles or electric vehicles. In lithium intercalation olivine compounds, the lithium diffusion along a channel is highly anisotropic which is mainly confined to the channel along the [010] direction. Thus, nanosheets or nanoplates with shortened Li ion diffusion distance along the [010] direction are enabled to accelerate the lithium intercalation rate and improve power density of the batteries. Herein, we report the production of high-quality thin LiMPO4 nanoplates with exposed {010} facets by a rapid supercritical fluid processing. The unique structure of the olivine nanocrystals with a shortened Li ion diffusion pathway allows fast extraction/insertion of Li ions in the structures. Thus, the LiMPO4 nanoplates provide high capacity and high rate capacity and excellent cyclability.

Disulfide-Bridged (Mo3S11) Cluster Polymer: Molecular Dynamics and Application as Electrode Material for a Rechargeable Magnesium Battery

Exploring novel electrode materials is critical for the development of a next-generation rechargeable magnesium battery with high volumetric capacity. Here, we showed that a distinct amorphous molybdenum sulfide, being a coordination polymer of disulfide-bridged (Mo3S11) clusters, has great potential as a rechargeable magnesium battery cathode. This material provided good reversible capacity, attributed to its unique structure with high flexibility and capability of deformation upon Mg insertion. Free-terminal disulfide moiety may act as the active site for reversible insertion and extraction of magnesium.

Synthesis, characterization and observation of antisite defects in LiNiPO4 nanomaterials

Structural studies of high voltage cathode materials are necessary to understand their chemistry to improve the electrochemical performance for applications in lithium ion batteries. LiNiPO4 nanorods and nanoplates are synthesized via a one pot synthesis using supercritical fluid process at 450 oC for 10 min. The X-ray diffraction (XRD) analysis confirmed that LiNiPO4 phase is well crystallized, phase purity supported by energy dispersive spectroscopy (EDS) and elemental mapping by scanning electron transmission electron microscopy (STEM). For the first time, we have carried out direct visualization of atom-by-atom structural observation of LiNiPO4 nanomaterials using high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) analysis. The Rietveld refinement analysis was performed to find out the percentage of antisite defects presents in LiNiPO4 nanoplates and about 11% of antisite defects were found. Here, we provide the direct evidence for the presence of Ni atoms in Li sites and Li in Ni sites as an antisite defects are provided for understanding of electrochemical behavior of high voltage Li ion battery cathode materials.

Supercritical fluid methods for synthesizing cathode materials towards lithium ion battery applications

Lithium ion battery materials improve the current technology to store electrical energy for the creation of green environment. The synthesis of lithium ion battery materials is crucial for energy applications in mobile electronic devices to plug-in hybrid electric vehicles. This review summarizes the recent progress made to synthesize lithium ion battery materials via supercritical fluid methods, and particularly, its application towards the synthesis of layered transition metal oxides, spinel structured cathodes, lithium metal phosphates, lithium metal silicates and lithium metal fluorophosphates. The structure, particle size, morphology and electrochemical properties of cathode materials are discussed. From the perspective of material synthesis, supercritical fluid methods are economical and have several advantages such as phase purity, morphology control and size tuning down to 5 nm, which would significantly impact the performance of lithium ion batteries.